Multifunctional Luminescent Solar Concentrator Integrating Optical Thermometry Based on PMMA/Eu^III-Complex Films for...

Multifunctional luminescent materials capable of simultaneously harvesting solar energy and monitoring environmental conditions are promising for next-generation smart windows. Here, we report transparent poly(methyl methacrylate) (PMMA) films doped with the Eu^III-based (Et₄N)[Eu(nta)₄] complex (nta^-: 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionate; Et₄N⁺: tetraethylammonium), designed to function as both luminescent solar concentrators (LSCs) and luminescent temperature probes. The nta^- ligand enables efficient sunlight absorption in the near-ultraviolet spectral range and sensitization of the Eu^III luminescence, affording overall emission quantum$\left(Q_{Eu}^L\right)$yields of up to 50% and sensitization efficiencies above 90%. The resulting PMMA films remain highly transparent (90-100% transmittance) and display homogeneous dopant dispersion, yielding intense red Eu^III emission upon exposure to sunlight and effective waveguiding. When coupled to a silicon photovoltaic cell and exposed to daylight, the PMMA:2%Eu^III film enhances current generation relative to an uncoated glass substrate, confirming its LSC capability. Moreover, the Eu^III 5D₀ lifetime is gradually quenched from 280 to 420 K (maximum relative thermal sensitivity of 4.7% K^-1 at 397 K), indicating that the film can operate as a temperature probe in locations exhibiting elevated temperatures (e.g., tropical countries, rooftops, parking lots). These results establish Eu^III-doped PMMA films as promising dual-function platforms for transparent, energy-harvesting smart windows with integrated optical temperature monitoring.